Contributions from DMS and ship emissions to CCN observed over the summertime North Pacific

Abstract

Measurements of cloud condensation nuclei (CCN) made over the remote North Pa-cific Ocean in July 2002 are analysed with concurrent measurements of aerosol num-ber, mass and composition. Overall the CCN are controlled by the sulphate, includingone case of particle nucleation and growth resulting from dimethyl sulphide oxidation that enhanced CCN concentrations. Hourly CCN concentrations are correlated withconcentrations of sulphate plus methanesulphonic acid (MSA) over the entire studyperiod (r2=0.43 and 0.52 for supersaturations of 0.34 and 0.19%, respectively), andare not well correlated with other organics (r2<0.2). One case study reveals elevatedmass and number concentrations of ultrafine and fine organic particles due to regional ship emissions, during which organic mass concentrations (see Fig. 2). In Fig. 7c,the 80–90 nm particle concentrations are correlated with CCN values (r2=0.39 and0.46 for supersaturations of 0.19 and 0.34%, respectively). The evolution of the timeseries and mass distributions of organics, sulphate and MSA over this timeframe indi-cate that the regional distribution of small, diffuse ship-sourced organic particles act as condensation sites for sulphur species, resulting in a subsequent increase in numberconcentrations of CCN. Direct emissions of organic particles may exert a strong controlon marine CCN concentrations once diffused into the marine atmosphere by acting ascondensation sites for biogenic and anthropogenic sulphur species.